For most pediatric sarcoma patients such as osteosarcoma (OS), despite successful management of the primary tumor through multimodality approaches, the development of metastases, commonly to the lungs, is the cause of death. Significant improvements in long-term outcome for these patients have not been achieved in more than 30 years. Furthermore, the long-term outcome for patients who present with metastatic disease is grave. This work has focused on the problem of metastasis in pediatric sarcoma patients. We believe that opportunities to improve outcomes for patients who present with metastases and those at-risk for metastatic progression require an improved understanding of tumor biology. Our focus on sarcoma metastasis will in many cases be complimentary and informative within the broader metastasis community; however, this focus is necessary specifically to improve outcomes for sarcoma patients. We have successfully built a platform for metastasis research in sarcomas, focused but not restricted to ezrin, that includes molecular biology, cellular biology, in vivo biology and translation to the human condition. As suggested above, the foundation of our success has been our development of transplantable murine and xenograft models of sarcoma metastasis. Our murine models have been used widely within virtually all sections of the Pediatric Oncology Branch and in the greater cancer research community. We first identified ezrin in a murine osteosarcoma model and have defined ezrin as causally associated with metastasis in that murine osteosarcoma model, in dogs with naturally occurring osteosarcoma, and, preliminarily, in pediatric osteosarcoma patients. We have assessed ezrin expression in over 5,000 human cancers, identified PKC isoforms as activators of ezrin, and linked ezrin expression with the early metastatic survival of cancer cells using novel imaging of single metastatic cells in the lung. We have used points of convergence between these three projects to prioritize and begin to test novel hypotheses. An exciting and unexpected finding that has come from this convergence has been that ezrin contributes to the efficiency of translation or translation initiation in metastatic cells. The link between ezrin, a protein not directly connected to the translational machinery, and translation initiation is novel and supports a growing hypothesis that suggests the importance of translation in metastasis. In all projects we pursue these hypotheses not only at the biological level but also with an eye toward a therapeutic end. We have now linked our studies of protein translation, and stress with the mTOR pathway. Using established tools in the lab we have developed a growing hypothesis that the classical inhibitors of mTOR (rapalogs) may exert their mechanisms of action through a novel and not previously described pathway, referred to as the unfolded protein response. This understanding is now being used in our lab to predict optimized treatment schedules for rapalogs and for the development of biomarkers that are predictive of therapeutic benefit in in cancer patients. Collaborative Research and Technology Transfer. Essentially all subprojects include collaborations both within and outside the Center for Cancer Research (CCR). In addition, our lab works closely with and provides reagent and approach support to several intramural and extramural investigators, the pharmaceutical industry, and cooperative groups including the Children's Oncology Group and the Sarcoma Alliance for Research Cooperation. Pharmaceutical collaborations are currently defined by MTAs that allow the evaluation of novel agents linked to metastasis biology within our in vivo models. Our proximity and close ties to the of the CCR-Comparative Oncology Program.